Method and apparatus for concentrating optical radiation using light trapping elements

ABSTRACT

A holographic planar concentrator for collecting and concentrating solar radiation with light trapping elements. A holographic planar concentrator (HPC) comprises a transparent planar plate with at least one holographic film mounted on the face of the planar plate and a solar energy collecting device attached to at least one edge of the planar plate with a reflective surface or coating mounted along the remaining edges of the planar plate. A holographic planar concentrator with light trapping elements reduces potential light losses, and the amount solar energy collecting material required while enabling a more uniform visual appearance and lower manufacturing and installation costs.

BACKGROUND

1. Field of the Invention

The present invention relates generally to the field of light collectors and more particularly to an optical concentrator that uses light trapping elements.

2. Description of the Prior Art

Due to the relatively high cost of solar collectors, sunlight is often focused or concentrated onto solar collectors to produce energy. Despite advances in the art that reduce the cost of solar energy collecting devices, these devices and the materials they are made of are still relatively expensive compared to other materials, so efforts are commonly made to minimize the amount of these needed for a particular application. The prior art contains numerous methods and arrangements designed to focus and concentrate optical radiation which use lenses, prisms, mirrors, or a combination of these for the purpose of heating fluids or generating electricity via the photo-electric effect.

One particular and promising approach for concentrating optical radiation taught by Rosenberg in U.S. Pat. Nos. 5,877,874 and 6,274,860 employs a holographic planar concentrator. U.S. Pat. Nos. 5,877,874 and 6,274,860 are hereby incorporated by reference. For solar energy applications, Rosenberg's concentrator generally uses a holographic optical film mounted on or affixed to one face of a highly transparent planar plate (such as a sheet of glass used in a window) along with a solar energy collecting device (such as a photovoltaic cell). The holographic film directs light into the transparent plate at such an angle that it totally internally reflects (Total Internal Reflection—TIR) within the transparent plate and travels through the plate to the solar energy collecting device, much the way light travels along a fiber optic. TIR is a well understood physical phenomena in which light traveling within a high index material strikes a surface between the high index and a low index material at an angle larger than some critical angle (relative to the surface normal) and this light is reflected by the surface such that it remains in the higher index material.

While Rosenberg concentrates on techniques such as holographic spatial and angular multiplexing as methods to reduce light loses from his optical concentrator, there are other simpler techniques that may be used to enhance the light trapping aspects of such a device and thereby improve its efficiency.

It would be advantageous to have a method and apparatus that uses simple optical techniques such as holographic optical concentrators, transparent plates and reflective elements to improve the efficiency and reduce the cost of a holographic planar concentrator. This would enable more people to use and benefit from our most abundant renewable energy source, the sun.

SUMMARY OF THE INVENTION

The present invention relates to using simple design elements such as holographic optical concentrators, transparent plates, and reflective elements to increase the amount of solar radiation arriving at a light collecting cell surface. The present invention mounts solar energy collecting devices along one edge of a transparent planar plate. The remaining edges of the plate have a reflective surface or coating.

It is an object of the present invention to increase the amount of light arriving at a solar collecting device.

It is another object of the present invention to reduce the amount of solar energy collecting material required.

It is another object of the present invention to reduce light loss within the device.

Finally, it is another object of the present invention to create a holographic planar concentrator with a uniform visual appearance.

The addition of reflective surfaces along edges of a transparent plate, except where a solar energy collecting device may be located allows mounting of a holographic film to the plate with less stringent alignment requirements between the film and the solar energy collecting device. This can simplify manufacture. Conversely a greater range of useful light input angles can be accommodated for any specific alignment between the holographic film and the solar energy collecting device.

If the device is used in a building integrated photo-voltaic (BIPV) application such as a multi-pane window or other glazing element, locating the solar energy collecting device along one edge of the transparent planar plate also means the solar energy collecting device is captured, with its associated wiring, within and along one part of the window frame. Capturing the solar energy collecting device within the window frame provides a uniform visual appearance which may improve the aesthetics of the BIPV product. In addition, by capturing the wiring within and along one part of the window frame, the transport, installation and maintenance/replacement of the product can be simplified because fewer connections between windows are necessary.

DESCRIPTION OF THE FIGURES

Attention is drawn to the following illustrations presented to aid in understanding the present invention.

FIG. 1 shows a perspective view of a prior art holographic planar concentrator (HPC) as it might look in a window frame, with the solar collecting energy device located along the bottom edge.

FIG. 2 is a cross-sectional view of a prior art holographic planar concentrator (HPC) showing a solar energy collecting device along the bottom edge.

FIG. 3 is a perspective view of an embodiment of the present invention including a holographic planar concentrator (HPC) with reflective surfaces along three edges and solar energy collecting device along the bottom edge.

FIG. 4 is a side view of an embodiment of the present invention including a holographic planar concentrator (HPC) showing the holographic film on one face (right), a solar energy collecting device along bottom edge, and the reflective surface along the top edge and one side.

FIG. 5 is a top view of an embodiment of the present invention including a holographic planar concentrator (HPC) showing the holographic film on one face (bottom), the reflective surface along two edges (the right and left side) and a solar energy collecting device seen through the transparent plate.

FIG. 6 is an exploded view of an embodiment of the present invention including a holographic planar concentrator (HPC) with the transparent plate, reflective surface three edges, solar energy collecting device along the bottom and holographic film on the front face.

Several drawings and illustrations have been presented to better explain the construction and functioning of embodiments of the present invention. The scope of the present invention is not limited to what is shown in the figures.

DESCRIPTION OF THE INVENTION

The present invention uses simple design elements such as holographic optical concentrators, transparent plates, and reflective elements to increase the amount of solar radiation arriving at a light collecting cell surface. Solar energy collecting devices can be mounted along one edge of a transparent planar plate, while the remaining edges of the plate can have a reflective surface or coating.

FIG. 1 shows a prior art method of constructing a holographic planar concentrator (HPC) (10) as it might appear inside a window frame. Three principle elements of a prior art holographic planar concentrator (10) are shown, a transparent planar plate (20) with a holographic film (15) attached to one face (22) and a solar energy collecting device (30) located along at least one edge (24). The holographic film (15) may have one or more repeated diffractive grating structures recorded onto it capable of bending light as desired. The transparent planar plate (20) has two opposing faces (22,23), each of which has a large surface area, and four edges (24,25,26,27) each of which has a small surface area, relative to the surface area of a face. The holographic film (15) bends light into the transparent planar plate (20) at such an angle that it totally internally reflects (TIR) upon striking either face (22,23) until the light hits the solar energy collecting device (30) or escapes the plate.

FIG. 2 shows a cross sectional view of the prior art holographic planar concentrator (10) which shows the holographic film (15) attached to one face (22) and the solar energy collecting device (30) located along the bottom edge (24) of the transparent planar plate (20).

FIG. 3 shows a perspective view of an embodiment of the present invention including a holographic planar concentrator with reflectors (12). Four elements are shown, a transparent planar plate (20) with a holographic film (15) attached to one face (22); a solar energy collecting device (30) located along one edge (24); and a reflective surface (32) or coating added to the remaining edges of the plate (25,26,27). The reflective surface (32) or coating, prevents light traveling within the plate due to total internal reflection from leaving the plate at an edge via transmission; instead the light is reflected back into the plate increasing the probability that the light will strike the solar energy collecting device (30). One type of reflective coating can be a thin metal layer or foil or a reflective stick-on tape. Other types include coatings that can be painted on or otherwise put on. Any type of reflective surface or coating is within the scope of the present invention.

FIGS. 4-5 show cross-section views of an embodiment of the invention which includes a holographic planar concentrator with reflectors (12). FIG. 4 shows the holographic film (15) attached to one face (22) on the right, and the solar energy collecting device (30) located along the bottom edge (24) of the transparent planar plate (20), plus the reflective surface (32) or coating located along the top edge (26). FIG. 5 is a top view of the embodiment of FIG. 4 showing the holographic film (15) on one face (bottom), the reflective surface (32) along two edges (the right and left side), and a solar energy collecting device (30) seen through the transparent plate.

FIG. 6 shows an exploded or assembly view of an embodiment of the invention including a holographic planar concentrator with reflectors (12). This view is useful in depicting how the various elements relate, including how the holographic film (15), the solar energy collecting device (30), and the reflective surfaces (32), or coatings, should be applied, mounted, or attached to the transparent planar plate (20).

An alternate embodiment of this invention uses a smaller solar energy collecting device (30) that only partially covers one edge (24) of the transparent planar plate (20). The remaining portion(s) of the partially covered edge (24) would then have the reflective surface (32) or coating added.

An alternate embodiment of this invention uses the solar energy collecting device (30) that covers two opposing edges (24,26) of the transparent planar plate (20). The reflective surface (32) or coating would then be added to the remaining opposing edges (25,27).

Another alternate embodiment of the invention maintains the location and orientation of the holographic film (15) attached to one face (22) of the prior art HPC as shown in FIG. 1, but has the solar energy collecting device (30) mounted on the opposite face (23), and adds the reflective surface (32) or coating to (all) the edges (24,25,26,27) that do not contain the solar energy collecting device (30). Alternatively, the device could have a solar energy collecting device (30) both on a face and one or more edges of the plate with the other edges having a reflective surface (32).

Several descriptions and illustrations have been presented to aid in understanding the structure and functioning of the present invention. One skilled in the art will realize that numerous changes and variations are possible without departing from the spirit of the invention. Each of these changes and variations is within the scope of the present invention. 

1. A holographic planar concentrator for collecting and concentrating optical radiation for solar energy applications comprising: a transparent planar plate; a holographic film mounted on at least one face of said transparent planar plate; a solar energy collecting device attached to at least one edge of said transparent planar plate; and, a reflective surface or coating attached to at least one edge of said planar transparent plate.
 2. The holographic planar concentrator of claim 1 wherein said transparent planar plate is glass or an optically transparent polymer.
 3. The holographic planar concentrator of claim 1 wherein said reflective surface or coating is attached to all edges of said planar transparent plate except said edge with said solar energy collecting device.
 4. The holographic planar concentrator of claim 1 wherein said holographic film contains at least one repeated diffractive grating structure.
 5. The holographic planar concentrator of claim 1 wherein said solar energy collecting device is selected from the group consisting of photovoltaic cells, thermally absorbing surfaces and fiber optic cables.
 6. The holographic planar concentrator of claim 1 wherein said solar energy collecting device is attached to only part of one edge of said transparent planar plate.
 7. The holographic planar concentrator of claim 6 wherein remaining portions of said one edge is covered by a reflective surface or coating.
 8. The holographic planar concentrator of claim 1 wherein said solar energy collecting device is attached to two opposing edges of said transparent planar plate.
 9. The holographic planar concentrator of claim 1 wherein said reflective surface is a metal foil.
 10. The holographic planar concentrator of claim 1 wherein said reflective surface is a paint.
 11. The holographic planar concentrator of claim 1 further comprising attaching a second solar energy collecting device to a face of said transparent planar plate opposed to said one face with said holographic film.
 12. A holographic planar concentrator for collecting and concentrating optical radiation for solar energy applications comprising: a transparent planar plate; a holographic film mounted on one face of said transparent planar plate; a solar energy collecting device mounted on an opposing face of said transparent planar plate; a reflective surface attached to at least on edge of said transparent planar plate.
 13. The holographic planar concentrator of claim 12 wherein said reflective surface is attached to all edges of said transparent planar plate.
 14. The holographic planar concentrator of claim 12 further comprising a second solar energy collecting device mounted on an edge of said transparent planar plate.
 15. The holographic planar concentrator of claim 12 wherein said solar energy collecting device is selected from the group consisting of photovoltaic cells, thermally absorbing surfaces and fiber optic cables.
 16. The holographic planar concentrator of claim 12 wherein said holographic film contains at least one repeated diffractive grating structure.
 17. A method for concentrating solar energy with a transparent planar plate comprising the steps of: attaching a holographic film to one face of said transparent planar plate; attaching a reflective surface to at least one edge of said transparent planar plate; attaching a solar energy collection device to at least one edge of said transparent planar plate.
 18. The method of claim 17 further comprising the step of attaching a solar energy collection device to a face of said transparent planar plate opposed to said one face with said holographic film.
 19. The method of claim 17 wherein said solar energy collecting device is selected from the group consisting of photovoltaic cells, thermally absorbing surfaces and fiber optic cables.
 20. The method of claim 17 wherein said transparent planar plate is glass or an optically transparent polymer. 